Bugzilla

Select email and use Menu app icon > Print or Ctrl+P
New Print Preview opens

This is not in a  separate window or tab and is fixed, so you cannot move it.
You cannot leave as it is and go back to read emails or access calendar or access anything.
With Print open you are prevented from doing anything in Thunderbird.

You cannot  go  back to list of emails and select to Print (Preview) another email, so being able to go through various emails or Calendar and stack up a separate list of windows which you will print at a later time.

Selecting Print to see preview now stops and prevents all access to Thunderbird.

Print needs to open in a new window, so it can be moved, so you can select other items that need to be printed.  So you can access Thunderbird to read emails etc.

Selecting Print should not block continued access to all of Thunderbird.

Select email and use Menu app icon > Print or Ctrl+P
New Print Preview opens

This is not in a  separate window or tab and is fixed, so you cannot move it.
You cannot leave as it is and go back to read emails or access calendar or access anything.
With Print open you are prevented from doing anything in Thunderbird.

You cannot  go  back to list of emails and select to Print (Preview) another email, so being able to go through various emails or Calendar and stack up a separate list of windows which you will print as a print job at a later time.

Selecting Print to see preview now stops and prevents all access to Thunderbird.

Print needs to open in a new window, so it can be moved, so you can select other items that need to be printed.  So you can access Thunderbird to read emails etc.

Selecting Print should not block continued access to all of Thunderbird.